Image reconstruction architecture

ABSTRACT

Methods and apparatus for reconstructing digitized images are provided that include an image reconstruction path that receives a digitized image and provides a processed RGB or CMYK image that may be printed or stored in memory. The image reconstruction path is configured to operate in either a multiple scan or single scan environment if the source of the digitized image is a scanner. A plurality of optional functional units in the reconstruction path can be controlled by user or internal controls. These functional units perform preliminary color adjustment, automatic deskew, background and dust removal, descreen, text detection and enhancement, color conversion, scaling, and color manipulation.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/314,573, filed 18 May 1999, now U.S. Patent No. 6,590,676.

FIELD OF THE INVENTION

The invention relates digitized image processing systems, and inparticular to image reconstruction architectures in which digitizedimages that are obtained from an image source, such as a scanner, areprocessed for output to an output device, such as a printer.

BACKGROUND

Image processing systems typically are used to adjust and correct imagesignals. For example, when printing a digitized image, such adjustmentsand corrections can include: color adjustment, deskewing, background anddust removal, descreening, text detection, text enhancement, colorconversion, scaling and color manipulation.

In most image processing systems, digitized image signal correctorsperform the adjustments or corrections based on processing parametersprovided by a system operator. The task of selecting the appropriateprocessing parameters for these correctors to achieve certain desiredoutput results is normally left to the operator, and is one of the moredifficult tasks in image processing. As the complexity of the imageprocessing model grows with advances in image processing technology,this task has become even more difficult.

For most adjustments or corrections, the operator typically does notwant to know about the particular processing parameters being used, butinstead wants to achieve the desired output results. Thus, it isdesirable to determine optimal processing parameters for digitized imagesignal correctors automatically to achieve specified output results foran image.

Examples of previously known automatic or semi-automatic imageprocessing systems include Spiegel et al. U.S. Pat. No. 5,615,282 andCapitant et al. U.S. Pat. No. 5,467,412. Such previously known systems,however, provide only limited image reconstruction capability. Forexample, such systems do not incorporate descreening or text detectionfacilities, and therefore an image reconstruction subsystem must beappended thereto. Further, such systems do not provide multiple datapaths (e.g., for single and multiple scans) and do not support bothcontone and 1-bit printing.

It would be advantageous to provide improved methods and apparatus forreconstructing digitized images.

SUMMARY

The invention provides improved methods and apparatus for reconstructingdigitized images. The invention processes one or more color formats(e.g., contone or 1-bit), and readily operates with image sources thatcan include both single and multiple scan systems. For purpose of thediscussion herein, multiple scan refers to systems that scan an imageonce per print separation. That is, for a CMYK printing system, theimage is scanned four times, and printing separations for C, M, Y, and Kare generated one by one. In contrast, single scan refers to copysystems that scan an image once for all print separations. Thus, for aCYMK printing system, the image is scanned once.

An exemplary embodiment of the invention provides an imagereconstruction path that receives a digitized image, for example, from ascanner or memory, and provides a processed RGB or CMYK image that maybe printed or stored in memory. The image reconstruction path isconfigured to operate in either a multiple scan or single scanenvironment when the source of the digitized image is a scanner. Withinthe image reconstruction path, there are a plurality of functional unitsthat can be controlled by user or internal controls, or that can beoptionally bypassed. These functional units provide any of preliminarycolor adjustment, automatic deskew, background and dust removal,descreen, text detection and enhancement, color conversion, scaling, andcolor manipulation. It will be appreciated by those skilled in the artthat other functions also may be provided.

An important feature of this architecture is that it is open-ended onboth the input and output ends. This means that with the appropriatecustomization, the architecture is ready to accommodate differentscanners at the input source and different printers at the outputtarget.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and features of the present invention can bemore clearly understood from the following detailed descriptionconsidered in conjunction with the following drawings, in which the samereference numerals denote the same elements throughout, and in which:

FIG. 1 is a block diagram of a digitized image processing systemincluding an exemplary image reconstruction path in accordance with thisinvention;

FIGS. 2 a and 2 b provide a processing flow diagram for an exemplaryimage reconstruction path that processes a multipass scanned image inaccordance with this invention; and

FIGS. 3 a and 3 b provide a processing flow diagram for an exemplaryimage reconstruction path within a single scan system in accordance withthis invention.

DETAILED DESCRIPTION

The invention provides improved methods and apparatus for reconstructingdigitized images. One important feature of the invention includes theability to process one or more color formats, e.g., contone or 1-bit,and to operate upon any image source. For purpose of the discussionherein, multiple scan refers to systems that scan an image once perprint separation. That is, for a CMYK printing system, the image isscanned four times, and printing separations for C, M, Y, and K aregenerated one by one. In contrast, single scan refers to copy systemsthat scan an image once for all print separations. For example, for aCYMK printing system the image is scanned once.

Referring to FIG. 1, a digitized image processing system including anexemplary image reconstruction path in accordance with this invention isdescribed. Image reconstruction path 10 accepts digitized image datafrom any of several sources, such as memory 14, video 12 (including datathat may be cropped 13 or otherwise processed) JPEG or other image data16 (such as GIF, TIFF, or PICT data), and RGB data 18 (e.g., from ascanner). In the case of video data, the system provides a mechanism, asis known in the art, for decompressing and deblocking the data,upsampling, and converting YUV to RGB 19.

Image reconstruction path 10 provides a front end capability forprocessing any type of digitized image data, although the internaloperation of the image reconstruction path is based upon the ultimatereceipt of digitized image data in an RGB format. Persons of ordinaryskill in the art will understand that image reconstruction paths inaccordance with this invention may be configured to operate on digitizedimage data in any format, and that the exemplary embodiment of theinvention is provided solely for purposes of illustration and exampleand is not intended to limit the scope of the invention in any way.

Image reconstruction path 10 is for a single scan system. Referring toFIG. 2, an appropriate image reconstruction path for a multipassarchitecture is now described. In the image reconstruction path, eachfunctional unit can be controlled by either of a user or by internalcontrols. Additionally, inclusion of each of the functional units in theimage reconstruction path is optional. The system has as its default anautomatic behavior which can be suppressed by the operator, either byturning some automatic functions ON or OFF, or by controlling theparameter settings for those functions. Accordingly, the apparatus andmethods in accordance with this invention provide the flexibility toinclude only those functional units of interest to the user. In anexemplary embodiment of the invention, the user may select the desiredfunctional units from a selection menu, such that the imagereconstruction path is readily reconfigured for each job.

Functional units within the image reconstruction path may include anyof:

-   -   Image rotation, duplexing, and tiling.    -   Preliminary color adjustment: this functional unit converts the        word size of the input image data as desired, and thereby        stretches the input data to a desirable dynamic range. For        example, the preliminary color adjustment functional unit        receives images data from the scanner at 8–12 bits per component        and returns 8-bit adjusted RGB values through the use of        one-dimensional curves. This is done by using a look-up-table        (LUT) sized by the number of possible input combinations, e.g.        4096 entries for 12 bit input.    -   Automatic deskew: this functional unit performs small angle        corrections for originals that are misplaced on the scanner's        glass during the scanning process. Such techniques are well        known in the art.    -   Background and dust removal: this functional unit removes noise,        dust, and uniform background, as requested by the user. Such        techniques are well known in the art.    -   Halftone detection: this functional unit detects areas of the        image that were originally printed using a halftoning process,        i.e., screen or error diffusion. One such halftone detection        process is described in Karidi U.S. Pat. No. 6,185,335, which        may be used to perform the function of this functional unit. The        descreening algorithm disclosed therein preserves soft edges.        Therefore, a preferred approach to halftone detection in the        exemplary embodiment of the invention marks all possible screen        areas for descreening unless sharp edge information is lost        thereby, e.g., boundaries of graphics and characters. In        exemplary embodiments of the invention, the halftone detection        procedure is applied to the intensity component Y of the image.        For each pixel, a decision is made whether the pixel is dark or        light relative to its neighborhood (e.g., a 5×5 neighborhood).        Each pixel is then considered with a surrounding window (e.g., a        9×9 surrounding window) and the size of the boundary set between        the dark and light classes is measured. A pixel is marked as a        halftone candidate only if the boundary size is less than a        probabilistic estimate.    -   Descreen: this functional unit reconstructs a contone image from        halftone data obtained during the halftone detection procedure        described above. An exemplary descreening process is described        in Karidi U.S. Pat. No. 6,222,641, which may be used to perform        the function of this functional unit. In this procedure, an        adaptive, edge-preserving low pass filter is applied to areas        that are marked as halftone. For each pixel that is marked as        halftone, a descreening kernel is applied to produce a smoothed        neighborhood of the pixel. Within this smooth context, locations        of those pixels whose values are within a certain threshold of        the current pixel are marked. These locations are used to build        a 0–1 mask that is applied to the low pass filter kernel. The        masked kernel is then convolved with the original, i.e.        non-smoothed, neighborhood of the current pixel. To avoid        over-smoothing, the original pixel value is restored if the        variation within the original window is smaller than one        threshold, or the number of marked pixels is smaller than        another threshold.    -   Text detection: this functional unit decides which parts of the        image contain text. In exemplary embodiments of this invention,        text comprises black text on a white background, although other        text detection schemes may be used. An exemplary text detection        process is described in Karidi U.S. Pat. No. 6,289,122, which        may be used to perform the function of this functional unit.    -   Text enhancement: this functional unit makes the text clear and        sharp. Exemplary embodiments of this invention only enhance        black text on a white background. An exemplary text enhancement        process is described in Karidi U.S. Pat. No. 6,185,335, which        may be used to perform the function of this functional unit. In        this exemplary embodiment of the invention, the ink component is        processed. To determine the ink level, e.g., 0–255, where        0=white, from the intensity level, a one dimensional look up        table (LUT) is applied. After resealing to the printing        resolution, the total amount T of ink is a surrounding window        (e.g., a 5×5 window) is measured. The number of pixels C that        are darker than the current pixel are counted. In simplified        form, a determination is made as follows: if (T>255× dot        factor×C), then put ink in the current pixel; otherwise leave        the pixel white. Text enhancement is preferably customized in        1-Bit systems, but need not in contone systems.    -   Color conversion: this functional unit converts from scanner        color space to the printer/host color space. In an exemplary        embodiment of the invention, the procedure interpolates a color        table from the input color space (i.e. RGB) to the output color        space (e.g. RGB or CMYK). The interpolation is either linear        (i.e., tetrahedral) or multi-linear. The color table is a        composition of the scanner calibration table (e.g., from scanner        RGB to a standardized or proprietary RGB used by the image        reconstruction path) and the printing engine's Color Rendering        Dictionary (CRD). The inputs to this functional unit include        text detection tags to ensure that black text is printed with        black ink only. For pixels that were marked as text, a three        dimensional table is not typically used. Rather, a separate, Y        to K, one dimensional table is used.    -   Scale: this functional unit selects the image up/down to map        print resolution and the user input. The exemplary embodiment of        the invention uses bi-cubic interpolation. Interpolation for        scaling is a well known technique.    -   Color manipulation: this function unit supports brightness,        color saturation, and contrast adjustments. These functions are        implemented through LUT's and linear operations (e.g. matrix        multiplication).

After the image data have been processed via the image reconstructionpath, the processed data are provided to an output module 20 thatformats the image data as RGB/CMYK data, as appropriate for the outputdevice. For example, the output device may be a computer memory 22, inwhich case the data may be maintained in an RGB format and/or compressedvia a compression module 21. If the image data are to be provided to aprinted by a printer 23, then the data are formatted as CMY or CMKY datafor use by the printer.

FIGS. 2 a and 2 b provide a processing flow diagram for an imagereconstruction path that correspond to a multi-scan system in accordancewith this invention. Thus, the processing flow shown on FIGS. 2 a and 2b is traversed four times for a CMYK printer, once for each of the fourseparations. During an image scan, an input signal 30 is provided to theimage reconstruction path. Preliminary color adjustment is performed 31,resulting in an R′,G′,B′ and a Y′ signal output 32. The imagereconstruction path performs a preliminary tagging operation 33 toproduce preliminary color tags 34.

The color conversion procedure 35 is next applied, resulting in acurrent color signal (CC) and an intensity signal (Y) 36. No use of R′,G′, B′ or Y′ information is made from this point on 37 in the imagereconstruction path because processing now proceeds for a current colorchannel in the multi-scan cycle.

The current color and intensity information, along with the preliminarytags, is provided to the dust and background removal function 38,resulting in a clean current color signal, a clean intensity signal, andclassification tags 39. Classification tags contain information relatedto color, e.g., an indication of how neutral a pixel is, whether a pixelis within an edge, or whether a pixel is in a high contrast region. Theclassification tags also record pixel locations for which backgroundremoval was applied.

The clean intensity signal is binarized for halftone detection 40,resulting in a binarized intensity signal 41. The binarized intensitysignal is then applied to the halftone detection function 42 to producehalftone tags 43.

The clean current color information is smoothed for descreening 44,resulting in smoothed current color information 45. The clean currentcolor information, smoothed current color information, and halftone tagsare applied to the descreening functional unit 46, resulting indescreened Current Color and intensity information and halftone tags 47.

The descreened intensity information and the classification tags arethen applied to the text detection functional unit 48, resulting in texttags 49. The text tags and scaled intensity information are provided tothe text enhancement functional unit 50, resulting in enhanced text andintensity information 51.

The scaled current color, intensity value of the enhanced text, and texttags are applied to a merge text function 52, resulting in reconstructedcurrent color and intensity information. The reconstructed current colorand intensity information is applied to the scale functional unit 54,resulting in scaled current color and intensity information 55. Thescaled current color and intensity information is applied to a halftonethreshold array or error diffusion functional unit 57. Typically, a1-bit system requires an error diffusion based halftone module, while acontone system requires a threshold array based halftone system.Thereafter, an output is provided 56 to the selected destination, e.g.printer or memory.

Referring now to FIGS. 3 a and 3 b, a processing flow diagram isdescribed for an image reconstruction path in a single scan system inaccordance with this invention. During a scan of an image by thescanner, an input RGB signal 150 is provided to the image reconstructionpath. Preliminary color adjustment is performed 151, resulting in anR′,G′,B′ and a Y′ signal output 152.

The R′,G′,B′ and Y′ information is provided to the dust and backgroundremoval function 153, resulting in clean R,G,B and Y signals and classtags 154. The clean intensity signal is binarized for halftone detection155, resulting in a binarized intensity signal 156. The binarizedintensity signal is then applied to the halftone detection function 157to produce halftone tags 158.

The clean RGB information is smoothed for descreening 159, resulting insmoothed RGB information 160. The clean RGB information, smoothed RGBinformation, and halftone tags are applied to the descreening functionalunit 161, resulting in descreened R,G,B and intensity information,halftone tags, and neutral tags 162. Neutral tags are similar toclassification tags and indicate whether a pixel is neutral or colored.

The descreened intensity information, class tags, halftone tags, andneutral tags are then applied to the text detection functional unit 163,resulting in text tags 164. The text tags and scaled intensityinformation are provided to the text enhancement functional unit 165,resulting in enhanced text and intensity information 166.

The RGB, intensity value of the enhanced text, and text tags are appliedto a color conversion function 167, resulting in either of RGB or CMYKinformation 168. The reconstructed RGB or CMYK information is applied tothe scale functional unit 169, resulting in scaled RGB and intensityinformation 170. There is no need to write this information to memory171.

The RGB/CMYK information is applied to a halftone threshold array orerror diffusion functional unit 172. Typically, a 1-bit system requiresan error diffusion based halftone module, while a contone systemrequires a threshold array based halftone system. Thereafter, an outputRGB/CMYK and text K layer signal is provided 173 to the selecteddestination, e.g. printer or memory.

The foregoing merely illustrates the principles of this invention, andvarious modifications can be made by persons of ordinary skill in theart without departing from the scope and spirit of this invention.

1. A method for reconstructing a digitized image provided by a scanneror an image memory, the method comprising: providing the digitized imageto an image reconstruction path for or producing RGB and CMYK outputimages, and that is selectively configurable to process images producedby single scan and multiple scan copy systems ; and providing the outputimages to any of a printer or an image memory.
 2. The method of claim 1,wherein the digitized image comprises an image that is stored in anyknown format.
 3. The method of claim 1, wherein the digitized imagecomprises any of video, image, and RGB data.
 4. Apparatus forreconstructing a digitized image provided by a scanner or an imagememory, the apparatus comprising: means for providing the digitizedimage to an image reconstruction path for or producing RGB and CMYKoutput images, and that is selectively configurable to process imagesproduced by single scan and multiple scan copy systems; and means forproviding the output images to any of a printer or an image memory. 5.The apparatus of claim 4, wherein the digitized image comprises an imagethat is stored in any known format.
 6. The apparatus of claim 4, whereinthe digitized image comprises any of video, image, and RGB data.